Session Initiation Protocol (SIP) is an emerging standard for Internet-based telephony and is supported by an increasingly wide range of IP phones, IP-PBXs, servers, media gateways, and switches.

SIP is becoming the go-to protocol for emerging IP telephony solutions. The various open source projects included in the SIP foundry community are all based around this request-response protocol that can initiate, alter, and terminate videoconferencing calls, Internet-based telephony calls, and other multimedia applications.